Liquor



Patented Aug. 2, 1927.

, l UNITED lSTATES PATENT OFFICE.

GEORGE A. RICHTER, or BERLIN, NEW HAMPSHIRE, AssIGNoE To BROWN COMPANY,

or BERLIN, NEW HAMPSHIRE, A CORPORATION or MAINE.

METHOD OF MAKING SULPHITECOOKING LIQUOR.

Application filed September 28, 1921. `Serial No. 503,846@

'lliis invention relates to the production of a 'liquor for cooking woodin the manufacture of chemical wood pulp.

Primarily the object of the inventionis 'to provide a process by `whichythere mayV be produced a calcium or magnesium bisulphite cooking liquorhaving a uniformly high'free sulphur dioxide content and a uniformpercentage of combined sulphur dioxide. Other objects of the inventionare to minimize the loss of sulphur constitiiients in the production ofthe liquor, to provide for the enrichment of the liquor with freesulphur dioxide or sulphurous acid, and to utilize the relief gases inthe formation of such liquor.

In carrying out my invention, l first produce what l term a raw acidliquor such as may be prepared by causing sulphur burner gases and waterto flow in countercurrent direction through absorption towers containinglimestone orother base material. Such a. raw liquor has a. relativelylow free sulphur dioxide content, and, according to my process, this isenriched by causing it to circulate in contact with a substantially pureor rich gas, until the free sulphur dioxide content is raised to therequired proi portion, to produce wl it may be termed a finishedacidliquoi.` To accomplish this result. rich or substantially pure gasis caused to flow in one direction through a series of towers containinga suitable inert interstitial or surface n'iaterial, andthe raw acidliquor is circulated throughsaid towers in the Opposite direction to theflow of the gas, the liquor Vbeing circulated rapidly several. timesthrough each tower before it reaches the .next tower in the series. The

enriching gas is preferably the relief gasy which is discharged from thedigesters during the process of digestion. One of the advantagesincident to the use of such relief gases is that theyrare practicallypure SO2 so that they may be employed with the greatest benefit inenriching the raw acid liquor.

Ordinarily, in the operation of apulp` an'iouut of relief gases ispermitted to escape.

a system such as l haveherein referred to, wherein the relief gases areutilized in the enriclnnent of the raw` acid liquor, such of the liquorin counter-cinrent iow to the` enriching gas. According to this method,although the main body of the acid liquor may be flowing in an oppositedirection to the vflow ofthe main body of-enriching gas from the reliefsystem of the digesters, utwerthelessp during their How, the liquor maybe caused at various points to be circulated in counter-current flow tothe gas in the various towers through which the` gas flows in series,lbut through which liquor is caused to be were. y

It is` quite evident `that the number of these towers utilized "in`enriching the raw acid liquor` maybe varied as'desired, but in generalit may be said that the greater the number `of such towers, the greaterwill be the enrichment of the acidliquor with free sulphur dioxide dueto the fact that counter-` current principles are most closelyapproximated. i On the accompanying drawings,- Figuref illustrates moreor less conven tionally and diagrammatically an apparatus or system forcarrying out my process.

`l`igure 2 illustrates in detail the main pipe for `thc raw acid liquorand the colinections between such enriching` towers.

`On this drawingnml indicates a digester of the Vusual type employed inthe manufacture of sulphite pulp so-called. `This digester is provided`with the usual relief pipe 2, through which the relief liquor and gasesmay be relieved from 'time to time as ordinarily; -This `pipe leads tothe usual separator 3 wherein the hot relief gas is separated from theliquor, the latter passing' downwardly through a pipe 4- to a towel' 5inwhich the relief liquor is freed of its residcirculated in multiple, asit pipe Vand some` of theV removed from such liquor. From this tower 5,the liquor, which has now been substantially V'freedv of its remaininggas (approxiv mately .75% to 85% having been liberated in apparatus 3),is deliveredV through a waste pipe 6. The hot relief gases, consistingof from 90% to 100% SO2, are delivered from the separator by a pipe 7.It is de- Y sirable to cool ythese gases before attempt is made' toutilize them in the enrichment'of the raw acid liquor, and consequentlyI have shown conventionally at 8 an indirect cooler by which these gasesare cooled preferably to a temperature of approximately 90O F. or below.The separator and the cooler may be of the ordinary construction. At 9 Ihave indicated conventionally a burner for the combustion of sulphur orsulphur-bearing material for the production of SO2. The gases deliveredfrom this burner are conducted by a pipe or conduit 10 to a coolerindicated as a whole at 11. Any suitable cooler may be utilized for thepurpose, but I have indicated conventionallyV a tower which may beprovided with a mass of inert interstitial material upon which water at-Vseasonable temperatures is sprayed from a nozzle 12 atthe end ofasupply pip-c 13. As the passes upwardly in counter-current flow to thewater, it is' cooled and is ready for delivery tothe absorption towers.For the purpose of cooling` the burner gases,

`I may utilize the cooling system illustrated in Patent No.1,4l69,959,granted to Gordon E. VVightman and myself on October 9, 1923. The gasesdelivered from the cooler consist of approximately 16% in ad- IniXturewith nitrogen and a small. percentage of oxygenand traces of othergases. At 111 and 15 I have indicated conventionally two of the usualabsorption towers einployed in theproduction of the raw acid liquor,such towers containing limestone,

dolomite or other calcium or magnesium bearing materials. The gas fromthe cooler l11 is delivered to the lower end of tower 14 through aconduit y16 by means of a pump 17, and passing upwardly therethrough isconducted by a conduit 18 to the lower end of tower 15. later isdelivered to the top of tower 15 by supply pipe 19, and the liquor fromthe base of said tower is forced by a pump 20 through pipe 21 to the topof tower 14. The delivery pipe 19 and the delivery end of pipe 21 aresupplied with usual spray nozzles as indicated at 22 and l Y Y 1,637,353

23. The bisulphite liquor, which I have termed y.the raw acid liquor, isconducted from the lower end of tower 14 by a conduit 24. This liquorcontains ordinarily about 2% treecSO2 and 1% combined SO2. The tail gasfrom tower emerges through lthe pipe 25, and a portion of this gas,which contains `little or no S02, is forced by a pump 26 through pipe 27to the lower end of the tower 5 for the purpose of sweeping from therelief liquor any free SO2 which may be therein. As previously stated,in `lieu of using the tail gas from the absorption tower for removingthe residual gas'in the relief liquor, other means may be utilized forthe saine purpose. As shown, a

conduit 28 conducts the gases .from the up-V per end of the scavengingtower v5 to the delivery 'end of the conduit 18, such gas containingapproximately 5% SO2. This .scavenging tower is ordinarily-at or belowVatmosqiheric pressure, therebypermitting a certain delinite removal ofsulphur dioxide from the relief li uor such as ordinarily cannot beremoved from the separator 3, due to the fact that this separator isordinarily under a delinite pressure varying from 1 to 20 poundsdepending upon the resistance encountered in passing the relief gasthrough the enriching towers to bedescrib'ed.

The raw acid liquor, on its way to a storage Vtank indicated at 29through the conduit 2l, is caused to absorb SO2 until it contains adefinite or predetermined high content ot free SO2. For this purpose` aspreviously stated, I employ the relief from the cooler 8 as it containsapproximately to 100% This is accomplished by providing a series ofenriching towers 30, 31, 33, the number of which may be varied asdesired. Each of these towers is provided willi a mass ot inertinterstitial material such, for example, as spiral brick, and they areso connected that relief gaswill pass through them successively. `Forthis purpose, a pipe tl-4l, leadingl from the gas cooler 8, deliverssuch gas to the lower end of the tower The upper end of tower 32E isconnected to the lower end of tower 32 by a gas conduit and similarlythe tower l2 is connected. to the tower 3l and the tower 81 to the tower30 by similar pipes 3G, 37. From the upper end of tower 30, a pipe 38conducts the tail gas, which contains approximately 16% SO2, to theconduit l0 where it is intermixcd with the burner gases containingapproximately a li ke amount ot SO2. Below each of the towers, there isa small tank associated therewith, these tanks-being` indicated `at 39,40, L1l and fel-2. They are introduced between sections of the conduit2-l for the raw acid liquor so that pools of such liquor vmay be formedand retainedtherein, the liquor 'Howing slowly from one tank to anotheruntil lli'i lili the gas passing therethrough.

it "is finally delivered to the storage tank 29 through which the acidliquor is pumped to a spray nozzle 45` at the upper end of the tower, sothat it may pass downwardly through the tower over the surfaces of theinert material and be brought into contact with the upwardly fiowingstreams of gas. From the lower end of the tower, the liquor is deliveredby a pipe 46 to thetank. Thus it will be seen that, as the liquor flowsslowly through the tanks 39 to 42 in series, which may be so locatedthat this ltakes. place by the action of gravity, the liquor may becirculated several. times through each of the towers into contact withthe gas therein. Hence, although the gas and the liquor pass in oppositedirections through the series of towers, nevertheless the liquor may becirculated from the pool below each tower several times through thetower. As it passesl through the towers, the acid liquor is increasinglyenriched with SO2, so that, by

the time it reaches the storage tank 29, it contains approximately 5%`free SO2, and 1% combined SO2. The relief gas, in flowing in theopposite directiontln-ough theseries of towers 33 to 30 inclusive, isgradual.- ly deprived of SO2, so that the tail gas, delivered throughthepipe 38, comprises aproximately or a little greater' percent-age of02 than is contained in the sulphur burner gases. f i

Instead of providing tanks as conventionally indicated at 39 to 42` theconduit 24 may be so formed as to provide pools of acid liquor. InFigure 2, for example, I have indicated a large conduit which may beapproximately l2 Vinches in diameter and which is indicated at 50.V Thisconduit is provided with transverse partitions 5l, dividing it so thatthere is a section associated with each of the enriching towers. Anoverflow seal 52 connects each pair of adjacent seetions, so that theliquor must pass through it before it is picked up by the pump 43 whichcirculates it through the associated tower. In this case, there islikewise provided means for the reception and temporary retention of apool of liquor from which the liquor may be circulated several timesthrough the tower associated therewith. When there is a small amount ofliquor passing through the system, as when a relatively small amount ofthe raw acid liquor is being made, each gallon of liquor may passthrough each tower several times before being delivered to the nexttower in series.

This affords repeated opportunity for the absorption of gas by theliquor in each tower, the limit of absorption being represented by thesaturation of the liquor under a given condition. Inasmuch as each towerin the series is a complete unit, it allows complete absorption underconditions which approximate quite closely a true counter-currentabsorption and ensures a high free sulphur dioxide content in the liquorleaving the towers. On the other hand, it is possible to treat a largevolume of liquor with great rapidity inasmuch as it re-circulatedseveral times before leaving any one of the towers.

Due to the rapid circulation of the liquor through each. of theenriching towers, there is'efi'ected a very eflicient distribution ofliquor over the inert surface Ymaterial contained in the tower. Such anefficient distribution cannot be obtained with a small volume of liquor'passing through the towers the more compl-ete will be the absorption ofv SO2 from the reliefl gas.

It is a well known fact that the rate of absorption of a soluble gas ina solvent increases rapidly when the velocity of the gas and of theabsorbing liquorI over a given area of surface material is increased.Hence, by increasing the volume of liquor passing through each tower ina given period of time, the efficiency of the tower and of its surfacematerial is increased. This is accomplished without sacrificing thebenefitsV derived from a counter-current system.

Inasniuch as each enriching tower has an independent connection with themain conduit 24, a temporary shut-down of any tower (due to accident orotherwise) will not interfere with the normal operation of the remainingportion of the system, for, if one tower is incapacitated, the liquor(which would normally flow through such tower) will merely pass to thenext` succeeding unit.

InV the normal operation ot' a digcster plant, the relief gas dischargedfrom the digesters fiuctuates considerably. At times there is a largevolume of relief gas, 'whereas, at other times, the relief gas is smallin volume or may even be cut oti' altogether. The system hereindescribed is so arranged that fluctuations of gas flow wil'l notinterfere with efiicient absorption of gas at all times, this being dueto the large volume of liquor which is present in the system atv anygiven time. That is, by providing the series of supply pools of acidliquor through which the liquor flows slowly, a given time period forany given volume of liquor to pass through the system may beestablished. This flow of liquor may be regulated according to theworking conditions of the particular mill in which it is installed,taking into account the nuinber of digesters which inay be connected toythe saine reliet systein. ln soins crises, it is desirable to provideineens for varying the speed of the circulating Vpuinps tor the vseveralenriching towers. This inay be accomplished in various ways7 as byproviding` enough variablesspeed inotors for the puinps 43, or the saineresult may be accomplished byfthrottling Valves 4:7 located in the pipesLl/l-V.

Inasnuich as the entire systein illustrated only conventionally andinore or less diagrainuuiticully, l'. have rnot attempted to show all otthe various valves, couplings, pumps, recording gages, ctc., with whichsuch a system is uornially equipped, but it will be understood, otcourse, that all ot such usuul instriuuentulities will be einployedas'nniy be needed; nor have l atu tenipted tovindicate thevarious'levels which the various instruinentalities inay be located northe relative sizes ot the Various instrunientalities. lt inay be pointedout, however', that the enrichiiig towers inay be `relatively sinall insize, say l() toet in length and G 'feet in diameter.

It is quite evident that various changes may be iuadc in the systein asconventionally illustrated and herein described, and that in SO,upwardly through a series' ot inasses ot conlined inert interstitialmaterial, inanitaining a supply pool ot said liquor associated with eachot said confined masses,

simultaneously circulating said liquor troni said poolsoownwerdlythrough said contined niasses et inert innitcrial associatedtherewith, and causing the liquor to flow progressively through thepools in opposite direction to the llow ot the gas and at a reteensuring the recirculation ot the liquor troni euch pool. tliroughthecorresponding tower, whereby such liquor is progressively increased intree SC2 content.

2. A process ot inaking :i vsulphite cooking liquor et' high -tree SO2content, which coniprises torining a raw acid liquor ot relatively lowtree SO2 content, passing a ges rich in S: successiveli7 thii'ough inertinterstitial inaterial in each ol a series ot towers, si nuiltaneouslypassing the raw acid liquor through each ot the towers in an oppositedirection and in countertiow to said gas,

inaiutainii'ig a pool ot liquor ttor each of said tewe,i's,jioui unichthe liquor is circulated to und hack Ytrom said towers, and producing atlow ot liquor trein pool to pool in opposite direction to the liowotgas,vwhereby such, liquor is progressively enriched with o. il processof inuling a sulphite cooking liquor ot high tree SO2 content, whichcon'iprises conducting sulphur burner gases through a series ot'`liinestonencontaining towers and conduct-ing water in theoppositedirection through seid towers to 'torin 'a raw acid liquor having arelatiif'ely low tree S02 content, pessii'ig the ruw scid liquorsiinultaneously through the towers oit a series of towers, having inertsui-'tace nuiterial,simul taneously therewith pessingdigester reliefdirection and in countcrtlow'to'said liquor therein, maintaining' asupply pool of liquor toi-'each oit said towers trom which pools theliquor is circulated through the associated towers and baci; to saidpools, and producing a flow oit liquor troni supply pool to supply poolin en opposite direction to 'the flow ot gas, whereby such liquor isprogressively enriched with tree SO2; and mixing thc tail ges trein saidlest-inentioned series ot towers with said burner gas, for theitorination oi' the liquor low in tree SOn A process ot meltingafcooking liquor' oit high tree SO2 contenuvwhich comprises conductingsulphur burner gases through a series ol liinestone-containing towersand conducting water in the opposite direction through said towers totorni a raw acid liquor having a relatively low tree SO2 content,separating troni the relief. liquor the gas relieved during` thedigestion oit sulphite pulp, passing such relief Agas through la seriesolf enriching towers in contect with inert surtaire n'iaterial,maintaining a supply pool of liquor tor each et said towers, producing e:flow o'i' liquor 'roin pool to pool in opposite di* rection to the tiowot gas, and circulating the liquor trein euch pool. through theassociated tower in countcrciiirrent Howto the gas therein, whereby suchliquor is progressively en; riched with tree S02, lrecovering S02 'fromsa id reliet liquor, and mixing such recovered S02 with the gases passedthrough said li iucstone containing towers at a point where the strengthet the SO2 in such decreased thereby. Y Y

-ln testimony 'whereof l have atliXed my signature.

e-nonenii. RICHTER.

gases is not

